dt-bindings: phy: add bcm63xx-usbh bindings

Document BCM63xx USBH PHY bindings.
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200720131209.1236590-2-noltari@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/brcm,bcm63xx-usbh-phy.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/phy/brcm,bcm63xx-usbh-phy.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: BCM63xx USBH PHY
+
+maintainers:
+  - Álvaro Fernández Rojas <noltari@gmail.com>
+
+properties:
+  compatible:
+    enum:
+      - brcm,bcm6318-usbh-phy
+      - brcm,bcm6328-usbh-phy
+      - brcm,bcm6358-usbh-phy
+      - brcm,bcm6362-usbh-phy
+      - brcm,bcm6368-usbh-phy
+      - brcm,bcm63268-usbh-phy
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    minItems: 1
+    maxItems: 2
+
+  clock-names:
+    minItems: 1
+    maxItems: 2
+    items:
+      - const: usbh
+      - const: usb_ref
+
+  resets:
+    maxItems: 1
+
+  "#phy-cells":
+    const: 1
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - resets
+  - "#phy-cells"
+
+if:
+  properties:
+    compatible:
+      enum:
+        - brcm,bcm6318-usbh-phy
+        - brcm,bcm6328-usbh-phy
+        - brcm,bcm6362-usbh-phy
+        - brcm,bcm63268-usbh-phy
+then:
+  properties:
+    power-domains:
+      maxItems: 1
+  required:
+    - power-domains
+else:
+  properties:
+    power-domains: false
+
+examples:
+  - |
+    usbh: usb-phy@10001700 {
+      compatible = "brcm,bcm6368-usbh-phy";
+      reg = <0x10001700 0x38>;
+      clocks = <&periph_clk 15>;
+      clock-names = "usbh";
+      resets = <&periph_rst 12>;
+      #phy-cells = <1>;
+    };